Single-gene mutations can be used to alter any given macromolecule or cellular process in the excitable cells. A proper collection of mutants should enable us to dissect the cellular structures of mechanisms of interest. The proposed research involves Drosophila mutants that have specific defects in membrane currents in nerve and muscle. Three different outward K+ current have been identified in Drosophila muscles: The transient IA, delayed rectification IK, and Ca++-dependent IC. These K+ currents are separately altered by Sh, eag. Hk and slo mutations. In the next year of support, we will concentrate on the single-channel and whole-cell measurements of cultured nerve and muscle cells to achieve positive identification of various channel types and their functional roles. Effects of specific mutations will be analyzed to probe common mechanisms shared among different channel types. In addition, voltage clamp experiments will be performed to analyze the dosage effect of Sh gene products on IA function. Different heterozygous combinations of various Sh alleles will reveal interactions among gene products and delineate their functional role within IA channels.